gutter overflow problem

[bertiebassett]

Whenever it rains heavily, the gutter from the roof at the back of our house overflows and water runs down the side of the house.
It is an 8cm semi-circle cross-section gutter, going into an 8cm downpipe (at one end of the gutter), draining nearly 100 square metres of roof.

I can't (easily) replace the downpipe, or add another, as it runs to the drains under a concrete floor, but I was considering increasing the size of the gutter, and using the same size downpipe.

As I see it, 8cm gutter has a cross-section of about 25cm squared, and the downpipe has about 50cm squared.
Couldn't I put an 11 or 12 cm gutter on, with a reducer to use the 8cm downpipe. This would have about the same cross-section as the downpipe, so couldn't it carry the same amount of water?

Or have I missed something important...

Thanks in advance!

 

[masona]

Or have I missed something important...

The first thing to do is check your downpipe is not blocked or at the top you may have a downpipe wire mesh blocked

 

[bertiebassett]

Thanks for the reply masona - I've checked and everything seems clear, but I think that the gutter just isn't big enough for the amount of water needing to be got rid of.

What I'm wondering is whether a bigger gutter, with the same downpipe, would help - or would that just mean that the downpipe would get too full and back up instead?

I've thought of putting another downpipe on the other end of the gutter and making a soakaway for that, but the water table is very high here, and I'm not sure of whether that would work. Belgian friends have suggested making a 30000 litre underground concrete container for it to run into, which I could use to save a few euros on my water bills, but that sounds like an awful lot of work, and I'd like to try less drastic solutions if possible....

 

[masona]

You can get wider gutter and I'm wondeing if the gutter is too low(?)

Are you getting a lot more rain in short time, if so, will need re-designing, have you tried with a garden hose or a small ball down the downpipe to see if it's clear, the most common problem blocked are on the joint and elbow etc Another downpipe will do it but need to level the fall both way

 

[bertiebassett]

There's no problem except when it rains very heavily - a normal shower drains no problem.
I don't think that the problem is with a blockage or the positioning of the gutter - i got (very!) wet the other day on a ladder in a torrential downpour checking it, and the gutter got totally full before it overflowed. I looked under the inspection for the main drain, and there was plenty of water gushing through there, so I can't imagine any blockage either.

As a second downpipe would be difficult to drain away, I think I'll try attaching a new 11/12cm gutter to the 8cm downpipe to see if that helps.

Thanks again, and I'll let you know how it goes when it next pees it down